Changing Adjustments to 19th Century SST

While there has been a great deal of discussion in other locations about possible urban heat island effect, there has been relatively little discussion about SST (sea surface temperature) adjustments and NMAT (night marine air temperature) adjustments. This is too bad. I’m not going to get into this, but there are some handy sources which I’ll direct interested people to and make a few short comments. 19th century temperatures are used to "verify" proxy models, but there are some curious inconsistencies between 19th century temperatures and proxy behavior, which I’ll not get into here, but made me go back to look at some of the 19th century adjustments. Generally, it worries me when "adjustments" become as large as the effect. One of the biggest changes in later IPCC reports resulted from new assumptions on 19th century use of wooden versus canvas buckets!. Parker, Folland and Jackson [1995] reported:

Overall global warming in SST between the 1860s and the 1970s is about 0.3 °C greater in the present analysis than in Folland et al. (1984), mainly owing to reduced early corrections applicable under the assumption of the predominant use of wooden buckets (Section 3).

You may recognize Folland as a major IPCC author (Folland et al. [2001] is sometimes the citation). SST sampling is not homogeneous – it changed from buckets to engine inlets – engine inlet temperature ran a little hotter. Both canvas and wooden buckets appear to have been used. There are millions of SST measurements and how the measurement was done is not known for most measurements (as far as I can tell.) There are two main adjustments in Folland et al. The first is a one-time adjustment for from buckets to engine inlets in December 1941. This is premised on a comparison between the "corrected" NMAT temperature [ I haven’t checked what these "corrections" are] and the uncorrected SST temperatures. Folland et al. express this as follows:

The abrupt change in SST in December 1941 coincides with the entry of the USA into World War II and is likely to have resulted from a realization of the dangers of hauling sea buckets onto deck in wartime conditions when a light would have been needed for both hauling and reading the thermometer at night.

This is exemplified in the follow graph:
Original Caption: Folland and Parker [1995] Figure 3. Annual anomalies from a 1951-80 average of uncorrected SST (solid) and corrected NMAT (dashed) for (a) northern (b) southern hemisphere, 1856-1992. Only collocated 5 deg. x 5 deg. SST and NMAT values were used.

The idea of an abrupt changeover seems a little weird to me. I’ve also seen reminisinces of an oceanographer taking about taking measurements in a research ship with steel buckets in the 1950s, so I’m not sure how realistic this assumption is. If the changeover were phased in, it would presumably have a material impact on the SST history. It seems like an important enough issue that it shouldn’t be glossed over. The big change in the 1995 Folland work is the conjecture that there was a changeover from wooden buckets to canvas buckets in the late 19th century, which caused a gradual "cooling" of measurements. This enabled them to depress 19th century temperatures a further 0.3 degree C and obtain a more compelling degree of temperature increase. The following graphic shows the difference:

I don’t plan to wade through this material but someone should. I haven’t looked yet to see what the NMAT correction is, but these things are always worth looking at. If Folland’s 1984 version or even a lesser adjustment were applied, then it makes a difference to calibration of the mutiproxy studies. An interesting collection of papers is here.

8 Comments

Steve,
Interesting stuff on the location of measurements. I would hope that any bucket of any mass would be allowed to sit in the water long enough to stabilize to that temperature instead of the ambient air which could be many degrees different from the water. Fat chance.
As for the actualy measurements themselves, I always have a problem with variations in something measured that is an order of magnitude smaller than the best accuracy of the measuring system.
In this case it is the many thermometers used. Is there any calibration/correlation data for the thermometers used for these measurements? I wouldn’t think so but one can always hope. Maybe some of the step changes are due to the widespread adoption of new and improved thermometers that you can actually read to better than 1 degree.
And before some one points out that many measurements average out the errors I would direct them back to their text books to discover that the reduction in error involves either measuring the same thing with many instruments or using the same instrument on many samples. It does not apply to many instruments measuring many different things under many different conditions by many different operators of various skill levels and that is exactly what we are talking about.

Has anyone thought to test the hypothesis by actually dragging a wooden bucket, a canvas bucket and a steel bucket behind a ship for an equal length of time, and then pulling them aboard and measuring the temperature in each?

Interesting hypothesis. But the specific heat capacity of water is so high that one would not expect any significant temperature difference due to varying collection methods an indeed that can be tested.

Furthermore if the war situation would preclude measuring SST by night then why not wait till dusk?

Another hypothesis might be that we are looking at the cause of the current temperature variation. Just variation in oceanic flow patterns.

I would suspect that the “problem” with a canvas bucket would be that water can evaporate from the surfaces of the bucket thus cooling the contents. This affect would then be a function of how big the bucket is and how long it takes to measure the temperature once the bucket is removed from the water. For steel buckets you’d have conduction and radiation. Wood buckets, however, would act pretty much as insulators.

Steve, I’m glad you bring this issue up. You’re right — there is an enormous amount of work to do to resolve this, but clearly this is a dominant factor in some of the data sets. I’m not sure I beleieve ANY of the adjustments, especially the more recent ones when satellite measurements (accurate, but measuring only skin temperatures) began to replace bucket-engine room measurements. Satellites will show warmer temperatures, but do we trust the adjustments? It’s like adjusting for UHI effects — we KNOW that UHI causes contamination, but how much? Simple adjustments (e.g., population) just don’t work. In the case of SST temps, sampling technique matters a great deal. How deeply did the bucket go? How long did they leave it one deck before measuring? How far in to the water did they did the thermometer? What was the air temperature, and the humidity? These and other details can affect the readings, and unfortunately they’re impossible to answer.

Another problem is the sampling density. A century ago there were large areas of the ocean with no measurements at all. I’ve seen some maps of sampling frequency at different times and there are very significant differences.

I think the mere idea that they can measure (or claim to measure) the temperature of an ocean to hundredths of a degree (see the diagram above) is simply ludicrous on its face. With modern instrumentation you wouldn’t get resolution like that from your bathtub.

Jeezuz, JohnA. This is a statistical site. Even if the individual thermometers were 1.0 or 0.5 degree accurate, if you sum enough of them, you can get valid expressions of difference in populations that are well less than the accuracy of an individual thermometer. Steve can explain it to you…

[…] Climate Audit. The absurdity of Team bucket adjustments had been discussed in two early CA posts (here, here, here ). In March 2007, after publication of Kent et al 2007 showed the prevalence of buckets […]